The subject matter disclosed herein relates to tension members such as those used in elevator systems for suspension and/or driving of the elevator car and/or counterweight.
Traction-driven belts typically include steel cord tension members that are encased in a polymer jacket that serves to maintain the proper cord spacing while preventing slippage of the cords during operation. The polymer jacket, typically an extrudable thermoplastic urethane, has a multitude of performance and manufacturing challenges. Friction, fire resistance, corrosion resistance, and other properties may need to be engineered into the jacket through the use of different polymers and additives. In order to provide the many necessary properties, there are often issues with material compatibility, mixing, settling, and other processing concerns. Further, extrusion profiles, temperatures, and production rates are all affected by these and can affect scrap rate. Such traction-driven belts may be utilized in elevator systems and other applications, such as grain elevators, hoisting and strapping applications and moving walkway systems.
Utilizing a composite type of construction, where the tension members are held in place by a yarn and a coating package or packages are then applied to the yarn and tension member assembly, can enable a construction that provides the necessary properties while mitigating some of the manufacturing challenges associated with a polymer extrusion process. Further, the use of low cost yarns and inexpensive coatings can result in a lower cost belt material. In order to maintain a low cost product, however, the yarn application process needs to use low cost materials and processes and the production rate needs to be quite fast. For this reason, commonly used processes such as knitting and weaving must be used. Further, the weft yarn spacing needs to be large enough to enable fast production to mitigate cost. This effectively limits the amount of yarn that can be used, which in turn limits the thickness and density of the belt. Wear resistance often becomes a limiting property of this type of construction in comparison to a polymer jacket structure.